Composite signaling circuits



May 29, 1923. 1,456,54Q

- B. P. HAMILTON I COMPOSITE SIGNALING CIRCUITS 7 Filed Aug. 29 1919 3Sheets-Sheet 1 Mme Legs L IN VEN TOR.

/ ATTORNEY May 29, 3923;

B. P. HAMILTON COMPOSITE SIGNALING CIRCUITS Filed Aug. 29 1919 3Sheets-Sheet 2 I Bi V EN TOR. fififfzmzifm ATTORNEY Patented May 29,E923.

UhlllTED PATENT C(DFFHQEQ BAXTER P. HAMILTON, 0F BROOYN, NEW YORK,ASSIGNOB) T0 ERICAN TELE- PHONE TELEGRAPH COMPANY, A CQRJPORATIQN OF NEWYGBK,

COMPOSITE SIGNALXNG CIRCUITS.

Application filed August 29, 1919. Serial lto. 320,705.

T 0 all whom it may concern Be it known that l, BAXTER P. HAMILTON,residing at Brooklyn in the county of Kings and State of New York, haveinvented certain Improvements in ()omposite Signaling Circuits, of whichthe following is a specification.

This invention relates to transmission circuits and more particularly totransmission circuits of the type in which a plurality of signalingchannels are imposed upon the same circuit.

it has been proposed in connection with a telephone transmission circuit(which may, if desired, be coniposited to provide the usual directcurrent telegraph channels) to superimpose upon such circuit anadditional signaling channel in which alternating currents of fairly lowfrequency are employed for transmitting the signals.

It is one of the objects of the present invention to provide a circuitarrangement by which the above results may be obtained, and which is soarranged that the alternating signaling current shall not interfere withthe terminal telephone apparatus. lhis objlzct, as well as others morefully appearing hereinafter, are accomplished in accordance with thepresent invention by providing a local balanced circuit with one side ofwhich the transmission line is connected and upon both sides of whichthe alternating signaling currents are applied, so that between the twosides of the balanced circuit points may be found which are neutral withregard to the signaling currents. The terminal telephone apparatus isconnected to these neutral points so that the signaling currents do notflow to the terminal circuit.

The invention may now be more fully understood by reference to thefollowing description when read in connection with the accompanyingdrawings, Figures 1, 2, 4, 5, 6, 7, 8, 9 and 10 of which constitutediagrams of diflerent modificationsof the invention, and Fig. 3 of whichis a schematic diagram illustrating the principle of certain of thecircuits.

A simple form of the invention is illus trated in Fig. 1, in which thetransmission line L is shown connected to one side of a local balancedcircuit comprising capacities l and 2 balanced against capacities 4 and6. Alternating signaling current from a source G is applied to the twosides of the local I resistance balanced circuit through similartransformers 3 and 5, so that at a given instant currents will tend toflow in the local circuit in the direction shown by the arrows. It thelocal circuit be considered alone independent of the line L and otherassociated equipment, it will be seen that neutral points exist at 7 and8 with respect to the oscillations applied through transformers 5 and6.. An artificial line N is connected to the lefthand side of the localbalanced circuit to balance the line L. H a proper balance is maintainedbetween the artificial line and the real line, the neutral points willstill exist at 7- and 8, and consequently no current from the source Gwill flow through the conductors 9 and IO-connected to said points. litthe conductors 9 and 10 be led to terminal telephone equipment asindicated at the 'j ack J, the telephone equipment will be unaflected bythe signaling current from the source G.

A modified arrangement by which the artificial line may be omitted isshown in Fig. 2. In this figure the local balanced circuit is arrangedas before, but the artificial line N is omitted, and instead a capacity11 and a resistance 12 are provided in. the primary circuit of thetransformer 5, these elements being adjustable so that the proper phaserelations and amplitudes of the potentials impressed upon the two halvesof the balanced circuit may be maintained.

The principle upon which this arrangement operates may be understoodfrom Fig. 3-in which R, is a resistance corresponding to the line L,while R and R are impedances corresponding to the capacities l and 2 ofFig. 2. Assuming a source of voltage E connected as shown, it will beseen that current from the source E, will tend to flow, part through theresistance R, in the direction indicated by the arrow, and part throughthe indicating instrument V and resistance R. Current may be preventedfrom flowing through the instrument V if an electromotive source E,beconnected across the circuit as shown in series with a resist- 'ance R,the electrornotive force E tending to cause current to flow through thebattery B, and resistance R, in the direction indicated by the arrow,and said source being so proportioned as to develop an electromotiveforce across the terminals of the indicating means V equalto andopposite in sign to that existing across the terminals by reason of thevoltage E applied through r.e sistance R and R.

Comparing this arrangement. with, that shown in Fig. 2, the operation ofthe latter circuit will at once be clear. At a given instant the voltageapplied to the transformer 3 tends to cause current to flow over line Lin the direction of the arrow and also through condensers 1 and 2 in thedirection indicated. At this same instant voltage may be applied throughthe transformer 5 of such value and direction as to equalize thepotential drop between points 7 and 8 due to the voltage applied throughcapacities 1 and 2. Consequently, if the phase relation isproperlyadjusted by capacity 11 and the amplitude is properly determinedby the impedance 12, points 7 and 8 will be neutral with respect tosource G and no current will flow over the conductors. 9 and 10 to thetelephone apparatus.

Fig. 4 illustrates a slightly modified arrangement of the invention asapplied to a telephone circuit composited for direct current Morseoperation. In this figure the Morse legs 13 and 14 are connected to thetelephone circuit L through impedances 15 and 16 adapted to prevent highfrequency telephone currents from flowing through the Morse legs,condensers 17 and 18 being provided to shunt to ground the higherfrequencies in the telegraph impulses transmitted from the Morse legs 13and 14.. Ca-

pacities 1 and 2 readily permit of the passage of telephone current buttend to prevent the transmission of Morse currents. Impedance elements19 and 20 and capacities 21 and 22 shunted to ground from points 7 and 8provide paths to ground for any telegraph currents which pass throughthe condensers 1 and 2, thereby preventing the telephone apparatusconnected to conductors 9 and 10 from'reaction of Morse currents.Alternating signaling currents from the source G may be applied throughtransformers 3 and 5 to the bridge circuits connected between points 7and 8, and 23 and 24 respectively. The latter bridge circuit includesinductances 25 and 26 and capacities 27 and 28 whereby the bridge istuned to the frequencies of the currents from the source G. Thetransformers 3 and 5 are so proportioned with reference to each otherthat the voltage impressed across points 7- rents to the transformer 3and 5 through as shown in Fig. 5.

eeasae parallel circuits as shown in Fig. 4 a series connection of thetransformers may be used The operation of the circuit of Fig. 5 is,however, in all respects similar to that ofv Fig. 4 and need not befurther described.

The arrangements shown in Figs. 4 and 5,. while not causing as severeloss in telephonic energy as the circuit shown in Fig. 1, have thedisadvantage that the phase relation and amplitude of the currentsapplied through the two transformers in the local balanced circuit willhave to be adjusted with variations in the impedance of the iezlternaltransmission circuit L. This will be clear from Fig. 3 since, assumingthe circuit to be balanced so that no current flows, through theindicating means V, if the resistance R be increased or decreased, itwill at once be necessary to vary the voltage of the source E in orderto maintain the balance.

An arrangement is illustrated in Fig. 6 which tends to obviate thisdifficulty and has the advantage that the local circuit will be at alltimes more nearly balanced regardless of the external impedance of thetransmission line. The telephone loss due to the balanced circuit willbe comparatively small due to the inductances 29, 30, 31 and 32. In thisarrangement, the transformers, by means of which the source G isassociated with the two sides of the balanced circuit, are each providedwith a plurality of primary and secondary windings. The two sets ofprimary windings in the circuit of the generator are designated as 33,34, 35, 33 and 37, 38, 39 and 40 respectively. The

.bridge circuit between the points 29 and 30 includes four secondarywindings of which 41 and 43 are associated with the righthand primarywindings, and t2 and 44 are associated with the lefthand primarywindings. Similarly a bridge circuit between points 31 and 32- includesfour secondary windings of which 45 and 4E7 are inductively related tothe lefthand primary windings and 46 and 48 are inductively associatedwith the righthand primary windings. Considering now the local balancedcircuit as being disconnected from the line L and from the terminalconductors 9 and 10., it will be seen that voltages are applied throughthe several windings of the two transformers, so that neutral pointsoccur at 7 and 8. If now the line L is connected to points 29 and 30 asshown, the energy supplied from the source G to the line L through,thebridge connection between points 29 and 30 will be derived one'halffrom the righthaud transformer arrangement and the other half from thelefthand transformer arrangement. Similarly the energy supplied to theline L through the bridge connected to points 31 and 32 is obtainedone-half from the righthand transformer arrangement and the otherissuance half from the lefthand transformer arrangement. It follows,therefore, that the line L, regardless of its external impedance,receives its energy equally from both sides of the local balancedcircuit, and does not, therefore, disturb the neutral condition of thepoints 7 and 8. The telephone apparatus associated with conductorsll and10, therefore, will not be afiected by the signaling current suppliedfrom the source G.

A slightly modified arrangement for securing even better balance asapplied to a composited telephone circuit is shown in Fig.7. In thisarrangement the Morse legs 13 and 1a are associated with the line L inthe same manner as illustrated in Figs. d and 5. points 29 and 30includes secondary windings a2 and 43 associated with the lefthand andrighthand primary windings 38 and 35 respectively. lnductances andcapacities are also included in the bridge connection to tune the sameto the frequency of the source G. Tn asimilar manner the bridge betweenpoints 31 and 32 in addition to inductances and capacities for thepurpose of tuning, includes secondary windings l5 and 46 associated withthe lefthand and righthand primary windings 37 and 3% respectively. litwill be seen that this arrangement is balanced in a manner similar tothat of hi 6 and consequently the points '2' and 8 will be neutral, sothat the terminal telephone apparatus connected to conductors 9 and 10will not be afiected by currents from the source G. The fact that thecomposite apparatus associated with the Morse legs 13 and it is bridgedacross the line L does not affect the operation of the circuit as thelocal balanced circuit including capacities l, 2, a and 6 remainsbalanced by reason of the peculiar transformer arrangement, regardlessof the character of the circuit connected to the righthand side of thebalanced arrangement at points 29 and 30.

A modified embodiment of the invention, somewhat analogous to thatillustrated in big. 1, is shown in Fig. 8. In this case the telephoneline L includes a three-winding transformer arrangement comprisingwindings 50, 51 and 52 and is balanced by an artificial line or networkN. leads 9 and 10 of the tele hone apparatus are then connected tomidpoints '8 and 8 of the windings 50and 52 in the telephone line. Thesource of signaling or telegraphic current G, together with thecontrolling key, is connected in series with the winding' 51, so thatwhen signaling current is'applied to the telephone line through thetransformer 50, 51, 52, points 7 and 8 are at substantially the samepotential and a minimum reaction of the signaling current upon theterminal telephone apparatus results.

The bridge connection between The terminal Since the terminal telephoneapparatus and the circuit including the source of the signaling currentG are conjugate, it is obvious that their connections may beinterchanged as illustrated in Fig. 9., in which the source G is appliedto the midpoints 7 and 8 of windings 50 and 52, while the terminaltelephone conductors 9 and 10 are connected to the windings 53. Theresult in this case is thesame as in F ig. 8, since the energy from thesource Gr divides equally between the line L and the artificial line N,so that no current isinduced in the winding 53 and consequently thetelephone apparatus is substantially unadected by the telegraphcurrents. v

The arrangement shown in Fig. 1G is substantially the same as thatillustrated in Fig. 9, but shows additional refinements ot the circuit,including an arrangement for receiving the telegraph signals. In thiscase the line L is provided with the usual composite apparatus UK, forsuperposing Morse signals upon the telephone line and is furtherprovided with the phantom coil PC, whereby the line may be used as oneside of a phantom circuit in a well-known manner. Coupled with the lineL, through the phantom coil PC, is a balanced circuit includingcondensers 53 and 541-, together with a winding 55 of a transformerincluding two additional windings, 56 and 57. The generator G may beconnected between points 7 and 8 of the balanced circuit, when the key Mis operated. Normally, however, an impedance element 58 is connectedacross these in ints over a back contact controlled by t e hey-K, theimpedance element being so designed as to have substan tially the sameimpedance as the generator G. An artificial line N, for balancing theline L, is associated with the balanced circuit through the transformer59. The terminal telephone leads 9 and 10 are connected to the winding5? of the three-winding transformer and a high pass filter HF isincluded in the terminal circuit. This filter is of the general typedescribedin the U. S. patents to George A. .Campbell, Nos. 1,227,113 and1,227,114, dated May 22,

v1917, and is so designed as to freely transand the energy therefromdivides between Nil the line L and the artificial line N, so thatsubstantially no energy is transmitted to. the terminal telephoneapparatus associated with the jack J. The telegraph receiving circuit 60is also in conjugate relationwith respect to the generator Cr and istherefore substantially unaffected by the current transmit-tedtherefrom. Alternating signaling or telegraph current received over theline L is transmitted through the phantom coil PC to the balancedcircuit, from which it is transmitted through the threeovindingtransformer arrangement 55, 56, 57 to the telegraph receiving circuitwhich is selective at this signaling frequency. 'lhe filter HF in theterminal telephone connection, ofi'ers a very high impedance to currentsof this frequency, however, so that they are not transmitted to theterminal telephone apparatus with sufficient amplitude to cause materialinterference.

By means of the arrangements of this invention alternating signalingcurrents may be applied to a composite circuit without atlecting thelocal terminal telephone apparatus associated therewith, and while theinvention has been shown embodied in certain arrangements which areconsidered most desirable, it will be obvious that the generalprinciples herein disclosed may be embodied in many other organizationswidely different from those illustrated, without departing from thespirit of the invention as defined in the following claims.

What is claimed is:

1. In a composite signaling system, a metallic transmission .line, alocal balanced circuit associated therewith, means to compensate "forthe connection of the lineto said balanced circuit whereby neutralpoints may be established, means to apply signaling currents to bothsides of said balanced circuit for transmission ove both sides of saidmetallic line, and terminal signaling apparatus connected to points ofsaid balanced circuit which are neutral with respect to said signalingcurrents. I

2. In a composite signaling system, a transmission line, a localbalanced circuit associated therewith, means to compensate for theconnection of the line to said balanced circuit whereby neutral pointsmay be established, means to apply signaling currents to both sides ofsaid balanced circuit for transmission over the line, and terminaltelephone apparatus connected to points of said balanced circuit whichare neutral with respect to said signaling currents.

3. in a composite signaling system, a local circuit comprisingtwosections, a metallic transmission line connected to one of saidsections, means to compensate for the connection of the line to saidsection whereby neutral points may be established between intenseneutral with respect to said signaling currents.

4. In a composite signaling system, a local circuit comprising twosections, a transmission line connected to one of said sections, meansto compensate tor-the connection of the line to said section wherebyneutral points may be established between the sections, means to applysignaling current to each of said sections for transmission over saidline, and terminal telephone apparatus connected to points between saidsections which are neutral with respect to said signaling currents.

5. In a composite signaling system, a local balanced circuit comprisingtwo sections, a transmission line connected to one of said sections, asource of signaling current, a transformer for each section, having asecondary winding in each section, the primary windings of saidtransformers being connected to said source, said secondary windingbeing divided and arran ed so that one half of each secondary isinductively related to one primary winding and the other half isinductively related to the other primary winding, whereby equal amountsof the signaling energy applied to the line is supplied over eachsection of said local circuit from each transformer, and terminalsignaling apparatus connected to points between said sectidns which areneutral with respect to the signaling currents supplied to saidsections.

6. In a composite signaling system, a local balanced circuit comprisingtwo sections, a transmission line connected to one of said sections, asource of signaling current, a transformer for each section, having asecondary winding in each section, the primary windings of saidtransformers beifig connected to said source, said secondary windingsbeing divided and arranged so that one half of each secondary isinductively related to one primary winding and the other half isinductively related to the other primary winding, whereby equal amountsof the signaling energy applied to the lineis supplied over each sectionof said local circuit from each transformer, and terminal telephoneapparat us connected to points between said sections which are neutralwith respect to the signaling currents supplied to said sec tions.

7. In a composite signaling system, a local circuit comprising twosections. a transmission line connected to one of said sections, meansto apply alternating signaling currentto each of said sections fortransneeaeefe mission over said line, terminal. telephone apparatusconnected to points between said sections which are neutral with respectto said signaling currents, a direct current telegraph apparatusassociated with said line, means to substantially prevent telephonecurrents or alternating signaling currents from affecting said telegraphapparatus, and

means to substantially prevent direct current telegraph impulses fromaffecting said 10 telephone apparatus.

In testi neny whereof, I have signed my name to this specification this27th day of August, 1919.

BAXTER P. HAMILTON.

